The \(J\hspace{-1.49994pt}/\hspace{-1.49994pt}\psi \hspace{1.49994pt}\)  was discovered in 1974 [1]}, [2]} and has
been studied in many generations of detectors. Due to its large
partial width to \(e^+e^-\) , the production cross section of \(J\hspace{-1.49994pt}/\hspace{-1.49994pt}\psi \hspace{1.49994pt}\)  in
\(e^+e^-\)  annihilation is about 90 \(\mu \) b. However, the actual
production rate suffers from initial state radiation and the
energy spread of the \(e^+e^-\)  beams [3]}. As a matter of fact,
the experimental production cross section of \(J\hspace{-1.49994pt}/\hspace{-1.49994pt}\psi \hspace{1.49994pt}\)  at BEPCII is
3500 nb with an energy spread of 0.9 MeV for the center-of-mass
(CM) energy [4]}.
The BEPCII [5]} is a symmetric \(e^+e^-\)  collider operating in
CM energies from 2 to 5 GeV, with design luminosity of
\(10^{33}~{\rm cm}^{-2}s^{-1}\)  at 3.77 GeV, the peak of the
\(\psi (3770)\)  resonance. The luminosity at 3.097 GeV, the \(J\hspace{-1.49994pt}/\hspace{-1.49994pt}\psi \hspace{1.49994pt}\) 
resonance, is about \(0.47\times 10^{33}~{\rm cm}^{-2}s^{-1}\) . The
energies of the \(e^+\)  and \(e^-\)  beams are known to 0.1 MeV and
they collide with a crossing angle of 22 mrad in the horizontal
plane, so the \(J\hspace{-1.49994pt}/\hspace{-1.49994pt}\psi \hspace{1.49994pt}\)  particle is basically static with a very
small boost which is known precisely. This is equivalent to a
production rate of 1600 Hz for \(J\hspace{-1.49994pt}/\hspace{-1.49994pt}\psi \hspace{1.49994pt}\)  events.
